Showing papers on "Zone plate published in 1978"

Multifocal zone plate

Abstract: A multifocal Fresnel lens construction suitable for use in optical systems with multifocal requirements. It is designed as a multifocal zone plate to allow an annular ring construction that isn't width limited by diffraction aberrations. This is accomplished by modifying the phase separating annular rings of a zone plate, with curved or inclined optical facets of varying refractive indices, which can then function as Fresnel rings corresponding to the different focal powers desired.

Comparison of Fresnel zone plates and uniformly redundant arrays

Abstract: Several imaging systems in laser fusion, a-beam fusion, and astronomy employ a Fresnel zone plate (FZP) as a coded aperture. The recent development of uniformly redundant arrays (URAs) promises several improvements in these systems. The first advantage of the URA is the fact that its modulation transfer function (MTF) is the same as the MTF of a single pinhole, whereas the MTF of an FZP is an erratic function including some small values. This means that if inverse filtering is used, the URA will be less susceptible to noise. If a correlation analysis is used, the FZP will produce artifacts whereas the URA has no artifacts (assuming planar sources). Both the FZP and URA originated from functions which had flat MTFs. However, practical considerations in the implementation of the FZP detracted from its good characteristics whereas the URA was only mildly affected. The second advantage of the URA is that it better utilizes the available detector area. With the FZP, the aperture should be smaller than the detector in order to maintain the full angular resolution corresponding to the thinnest zone. The cyclic nature of the URA allows one to mosaic it in such a way that the entire detector area collects photons from all of the sources within the field of view while maintaining the full angular resolution. If the FZP is as large (or larger) than the detector, all parts of the source will not be resolved with the same resolution. The FZP does have some advantages, in particular its radial symmetry eases the alignment problem; it has a convenient optical decoding method; and higher diffraction order reconstruction might provide better spatial resolution.© (1978) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Micro-Fresnel zone plates for coded imaging applications.

Abstract: Design considerations and fabrication procedures for Fresnel zone plates appropriate for high-resolution coded imaging of x-ray and particle emission from laser produced plasmas are presented. Fabrication results for free standing zone plate structures of high Z material (gold), large zone number (100

Analysis and interpretation of soft X-ray photographs of coronal active regions taken with Fresnel zone plates

Abstract: Soft X-ray photographs of the Sun taken at O vii 21.6 A and in a spectral band ranging from 13.2 to 22.1 A have been analysed in order to establish spatially resolved maps of temperature and emission measure for several active regions in the corona. The photographs were taken on 11 March, 1971, and on 2 March, 1972, with Fresnel zone plate cameras which were flown on ESRO and NRL sounding rockets.

Resolutions in imaging with Fresnel zone plate.

Abstract: A coarse Fresnel zone plate (FZP) may be used as a large-area coded aperture for imaging incoherent sources. The longitudinal and lateral spatial resolutions are discussed on the basis of experiment using an FZP having 18 or 19 zones as an aperture. In this paper, it is then shown that the lateral spatial resolution is about 5 mm and the longitudinal is about 1 cm, respectively and it is appropriate to use the longitudinal resolution factor 3.7 as a guide to know the tomographic effect. These results may be extended for imaging incoherent gamma-ray sources. According to our experiments, radioactivity of several tens of a millicurie is necessary for imaging with 99mTc, when using X-ray film as a detector. Therefore, it is important to improve the detector in order to apply to the human organ imaging generally.

Preparation of zone plate

Abstract: PURPOSE:To easily prepare a plate having no sprious ring by forming a hologram without use of a transluscent mirror, after the beam of a coherent flux of light is enlarged, to record the concentric interference fringes of two kinds of spherical waves.

A fundamental study on imaging with an off-axis Fresnel zone plate.

Abstract: An off-axis Fresnel zone plate, through use of a halftone screen to introduce a spatial carrier frequency, can be used as a large-area, coded aperture for imaging incoherent radiation sources. This paper discusses the structure of off-axis Fresnel zone plate as an aperture and the mentods of imaging from the viewpoint of the spatial resolution by optical simulation, appending some examples of objects, holograms and reconstructed images. It is then concluded that the off-axis Fresnel zone plate having D (diameter) = 5.8 cm and nuc (spatial center frequency) = 23 l/cm is sufficient for the reconstructed images.

Producing of zone plate

Abstract: PURPOSE:To produce a spherical zone plate at a low cost by irradiating the hologram, which is formed by a first spherical wave and a reference wave, with the same wave as the reference wave to record a concentric fringe pattern which is formed by interfering with a second spherical wave having a different radius of curvature.

Phase Quadrature Techniques in Holography

Abstract: Various extensions of Keating’s complex (sine-cosine) hologram procedure are discussed. These include phase-quadrature zone plates and gratings and extensions of the use of quarter-wave plates in applications involving circularly polarized waves.